The present invention is directed to an electrostatic chuck for holding a substrate in a process environment.
In integrated circuit manufacture, chucks are used to hold semiconductor substrates to prevent movement or misalignment of the substrate during processing. Electrostatic chucks, that use electrostatic attraction forces to hold a substrate, have several advantages over mechanical and vacuum chucks, including reduction of stress-related cracks caused by mechanical clamps; allowing utilization of a larger portion of the substrate surface; limiting deposition of corrosion particles on the substrate; and allowing use of the chuck in low pressure processes. A typical electrostatic chuck includes an electrically conductive electrode with an electrical insulator thereon. A voltage source electrically biases the substrate with respect to the electrode. The insulator prevents the flow of electrons therethrough, causing opposing electrostatic charge to accumulate in the substrate and in the electrode, thereby generating an electrostatic force that attracts and holds the substrate onto the chuck.
A typical electrostatic chuck comprises a metal electrode covered by a thin polymeric insulator layer. The thin polymer layer maximizes electrostatic attractive forces between the substrate and the electrode. However, when the substrate held on the chuck breaks or chips to form fragments having sharp edges, the substrate fragments puncture the polymer film exposing the electrode of the chuck, particularly when the polymer is soft and has low puncture resistance at high processing temperatures. Exposure of the electrode at even a single pinhole in the insulator can cause arcing between the electrode and plasma, and require replacement of the entire chuck. Polymer insulators also have a limited lifetime in erosive process environments, such as processes using oxygen-containing gases and plasmas. In these processes, the insulator can be eroded by the erosive process gas and the resultant exposure of the electrode results in failure of the chuck during processing and loss of the entire substrate at a significant cost. It is also desirable for such polymeric insulator layers to provide sustained operation at elevated temperatures, preferably exceeding about 175.degree. C., and more preferably exceeding 200.degree. C.
In one solution for increasing the puncture and erosion resistance of the insulator, a hard ceramic layer is formed over the electrode.
For example, commonly assigned EP 635 869 A1 discloses an electrostatic chuck that comprising a polymeric dielectric layer with a protective ceramic overcoat of Al.sub.2 O.sub.3 or AlN. In another example, U.S. Pat. No. 5,280,156 to Niori discloses a ceramic dielectric layer covering an electrode of an electrostatic chuck. In yet another example, U.S. Pat. No. 4,480,284 discloses a ceramic layer made by flame spraying Al.sub.2 O.sub.3, TiO.sub.2, BaTiO.sub.3, or a mixture of these materials over an electrode, and impregnating the pores of the ceramic dielectric with a polymer. However, there are several problems with these ceramic structures. One problem with ceramic overlayers is that the volume resistivity of ceramic layers generally decreases to values less than 10.sup.11 .OMEGA.cm with increasing temperature resulting in unacceptable current leakage from the electrodes of the chuck at high temperatures. Another problem is that the ceramic and polymer layers often delaminate from one another, particularly when the thermal expansion coefficients of the layers is mismatched.
Yet another problem with the hard ceramic layers occurs because it is often necessary to cool the substrate when the substrate is being processed in plasma processes. Bombardment by high energy plasma ions cause heat buildup and thermal damage to the substrate and chuck. Conventional chucks utilize cooling systems which hold coolant between the substrate and the insulator of the chuck to cool the substrate. However, it is difficult to form a seal between the hard ceramic coatings and the peripheral edge of the substrate causing coolant to leak from the grooves of the chuck, and resulting in non-uniform temperatures across the substrate. Also, it is difficult to machine the ceramic layers to form coolant holding grooves or coolant inlet apertures that do not have rough edges and corners. The rough edged grooves easily scratch and damage the substrate held on the chuck. Furthermore, such cooling systems can be inefficient when used on ceramic chucks because the highly thermally insulative ceramic insulator can impede the transfer of heat from the substrate to the chuck.
Thus, it is desirable to have electrostatic chuck that is resistant to failure from puncturing by sharp fragments and particles, and from failure by erosion in erosive process environments. There is also a need for an electrostatic chuck that is capable of sustained operation at elevated temperatures, preferably exceeding about 200.degree. C. It is also desirable to have a chuck which allows coolant to directly contact the substrate, without causing excessive coolant leakage from the periphery of the chuck. There is a further need for a fabrication process for providing a thin insulator that maximizes electrostatic attractive force, a strong bonding of the insulator to the electrode, and a conformal insulator layer with smooth edged coolant grooves and apertures.